Field of the Invention
The present invention relates to methods for making solid state devices and, more particularly, to methods for making a sloped insulator structure overlaying a semiconductor wafer as used in solid state devices.
Background of the Invention
Recent developments in the art of solid state electronic devices have created a need for a method of making a sloped insulator structure overlaying a semiconductor wafer. For example, a sloped insulator charge coupled device has been investigated having improved transfer times between adjacent wells. The improved response times of the sloped insulator charge coupled device are a consequence of the sloped disposition of the electrodes with respect to the interface of the semiconductor wafer and an insulation layer. This sloped disposition provides a lateral, or drift field, component in the electric field produced by the elements of the electrode array. The drift field component operates as a mechanism for transferring charge carriers between adjacent wells of the charge coupled device. The sloped attitude of the elements of the electrode array is achieved by supporting these elements on sloped portions of the insulation layer. Therefore, in the manufacture of the device, the controlled production of sloped areas over selected portions of the insulation layer is essential.
It was recognized that it would be desirable to employ as few processing steps as possible to produce an overlying insulation layer with selected areas having a controlled slope. Accordingly, there was a need for an efficient method of making an insulation layer having selected areas of a predetermined slope.